A joint capsule is a watertight sac that surrounds a joint. In the shoulder, the joint capsule is formed by a group of ligaments that connect the humerus to the glenoid. These ligaments are the main source of stability for the shoulder. The ligaments include the superior, middle, and inferior glenohumeral ligaments, which help hold the shoulder in place and keep it from dislocating.
The shoulder also includes a rotator cuff, which is a group of tendons and muscles connecting the upper arm (humerus) to the shoulder blade (scapula). The rotator cuff tendons cover the shoulder joint and joint capsule and provide stability to the shoulder. The muscles allow the shoulder to rotate. The rotator cuff tendons also encircle the humeral head (ball) and help to keep the humeral head in the glenoid (socket) when the arm is elevated. These tendons also help to rotate the humerus on the glenoid so the arm can be raised. Without normal function of the rotator cuff, the humeral head may move upward out of the glenoid socket, which makes it difficult or impossible to raise the arm up. If a conventional joint replacement is used in this situation (i.e., where the rotator cuff is damaged or lacking), though there may be some pain relief, the humeral head usually remains upward out of the socket and elevation of the arm is impossible. Thus, a reverse shoulder replacement is typically indicated for situations such as this. A reverse shoulder replacement places an artificial ball where the normal glenoid socket is located, and an artificial socket where the normal humeral head is located. Reverse shoulder replacements can change the mechanics of the shoulder and enable the artificial joint to function when the rotator cuff is either absent or when there is significant bone loss.
The present disclosure provides shoulder replacements and methods that can be used to stabilize the replacement in instances where using a traditional shoulder replacement would be difficult.